It is pointed out that the divergence in Yukawa's theory of βdisintegration can be removed by charge and mass renormalizations, whereas in conventional Fermi's theory this is not the case. From the known interaction constants for nuclear β-decay, for μ-e decay and for the interaction of μ-mesons with nucleons, it is found that the life time of the intermediary meson should be of the order 10-16 sec. We can therefore consider this intermediary meson as a new particle which has not been observed experimentally owing to its extremely short life time. Best agreement with experiment is obtained if the intermdiary meson is pseudo-vector in nature and under pseudo-vector interaction with the Fermi fields, those types of interactions being excluded which lead to divergent results for observable effects.